ABSTRACT: Cubic saw-tooth specimens are made by using cement mortar filled with material. Considering the effects of different factors stress on the mechanical properties of rock, three factors are considered in this paper: three kinds of filling degrees (0,0.5,1), three kinds of asperity angles (25°,40°, 55°), two kinds of filling material(white cement, gypsum). The direct shear test is carried out under different normal stresses (30kN,50 kN,80 kN,120 kN). The results indicated that, when the normal stress is low, the peak shear strength of white cement filling and gypsum filling no obvious difference. The peak shear strength for filled joints decreases with the increase of filling degree. The asperity angle is in direct proportion to the peak shear strength. Besides, the normal stress is in direct proportion to the peak shear strength. In addition, three factors (filling degree, asperity angles and filling material) play an important role in the failure mode.

ABSTRACT: Anisotropy in the mechanical properties of rock is often attributed to layering or mineral texture. Here, results from a study on mode I fracturing are presented that examine the effect of layering and mineral orientation fracture toughness and roughness. Additively manufactured gypsum rock was created through 3D printing with bassanite/gypsum. The 3D printing process enabled control of the orientation of the mineral texture within the printed layers. Three-point bending (3PB) experiments were performed on the 3D printed rock with a central notch. Unlike cast gypsum, the 3D-printed gypsum exhibited ductile post-peak behavior in all cases. The experiments also showed that the mode I fracture toughness and surface roughness of the induced fracture depended on both the orientation of the bedding relative to the load and the orientation of the mineral texture relative to the layering. This study found that mineral texture orientation, chemical bond strength and layer orientation play dominant roles in the formation of mode I fractures. The uniqueness of the induced fracture roughness is a potential method for the assessment of bonding strengths in rock.

ABSTRACT: The dissolution of rocks in underground flow paths is transport-controlled if their dissolution rates are relatively high, while the dissolution is reaction-controlled if their dissolution rates are relatively low. Transport-controlled dissolution is a common process in the formation of gypsum karst and oil reservoir acid stimulations. As an initial step to understand groundwater flow and dissolution in fractures and in wormholes, pipe flow is used as a simplified representation of groundwater flow. The extended Graetz solution was developed by Li and Einstein, 2017 to simulate the transport-controlled dissolution process when water flows through a tube in gypsum. This model can predict both the effluent concentration and the evolving geometry of the tube during the dissolution process. This paper focuses on the experimental validation of this model. An effluent chemistry monitoring system (ECMS) was developed and integrated in the triaxial system at MIT. Flow tests were conducted with cast gypsum tubes in this triaxial system. The experimental results of the effluent chemistry and tube geometries confirmed the validity of the extended Graetz solution.

ABSTRACT: When anhydrite dissolves upon contact with water, the sulphate and calcium ions in the pore water can lead to precipitation of gypsum. This anhydrite to gypsum transformation (AGT) results in an increase in the solid volume by 61% and in a decrease or increase in the pore volume. On a macroscopic scale the so far insufficiently understood phenomenon “swelling of anhydritic rock” is observed, which is known to cause massive damage to underground constructions, such as tunnels. This contribution focuses on one specific aspect of AGT, the precipitation of gypsum directly on the surface of the dissolving anhydrite, which creates a diffusion barrier for the dissolving ions and slows further anhydrite dissolution down (hereafter referred to as “self-sealing”). The development of such gypsum layers on anhydrite is investigated experimentally by storing natural rock specimens consisting of 96%-99% anhydrite in water and observing the thickness of the developing gypsum layer optically via photography during the tests and via microscopic analysis after drying of the samples. The measured thicknesses corresponded well to the amount of precipitated gypsum determined post test via thermogravimetric analysis and to predicted values which were calculated with an existing kinetic model. The plausibility of this model could thus be verified so far. As anhydrite comes into contact with water it will begin to dissolve under most circumstances below 40°C (at atmospheric pressure). As the saturation concentration with respect to anhydrite (c eq,A ) is higher than that of gypsum (c eq,G ), anhydrite dissolution results in oversaturation with respect to gypsum, thus triggering growth of gypsum crystals, whereby the solid volume of gypsum is 61% higher than that of anhydrite due to the additional water molecules bound in the crystals. The chemical reaction from anhydrite (CaSO 4 ) to gypsum (CaSO 4 • 2H 2 O) will be referred to here as AGT (Anhydrite – Gypsum Transformation) and can be formulated in short as CaSO 4 + 2H 2 O ? CaSO 4 • 2H 2 O.

Abstract In this paper, the three dimensional Particle Flow Code (PFC3D) with a newly developed contact model which can properly consider the contribution of moment to contact normal and shear stresses and the condition at which the contact bond fails was used to investigate the cracking process of rocks containing single flaws and under uniaxial compression. The new contact model was first validated by using it to simulate the experimental cracking process of gypsum containing pre-existing single flaws at different inclination angles. Then the influence of flaw shape (length and thickness) on the cracking process was systematically studied and the key features were identified based on the simulations. The results indicate that the first cracks (usually called primary cracks) initiate from the boundary of the pre-existing flaw and are always caused by tensile failure, and the secondary cracks first emanate from the tips of the pre-existing flaw due to shear failure and then develop to a mixed shear and tensile cracking zone. 1. INTRODUCTION The initiation, propagation and coalescence of cracks dominate the deformability and strength of rock. Therefore, extensive experimental and theoretical research has been conducted on the cracking process of rock. The cracking process of samples containing flaws under uniaxial compressive loading provides insightful understanding of the cracking of natural rocks and thus has been studied extensively by researchers using rocks and manmade materials. The term flaws refer to preexisting cracks or holes in the rock specimens. The results indicate that tensile wing cracks are always found to be the first cracks to initiate from the flaw boundary and continued loading leads to initiation of a secondary group of cracks that may be a combination of tensile and shear cracks. However, the types and mechanisms of the new cracks that developed after the tensile wing cracks are often hard to be categorized, and the stress field inside the specimen is never fully revealed [1]. Most researchers simply describe them as secondary cracks without implying the mode of crack initiation. In this way the first cracks are commonly referred as primary cracks. So the words "primary" and "secondary" simply imply a temporal relationship.

Abstract Gypsum (a mix of Hydrocal B-11 and Diatomaceous Earth) is used by the MIT rock mechanics group as a model rock material. Unconfined compression tests on pre-cracked specimens with high speed camera observation showed macro-cracking processes of gypsum similar to other materials; however in contrast to the other materials, no microcrack process zone could be observed. On the other hand, environmental scanning electron microscope (ESEM) observation of gypsum showed limited micro-cracking preceding the crack initiation. This indicates that a microcrack process zone in gypsum might exist but it is not visible in high speed camera photography because of the scale. It was therefore decided to use acoustic emission (AE) to determine if such microcracks occur. To this end, prismatic specimens containing pre-existing flaws were tested under uniaxial compression, and the cracking process was monitored with both AE and high-speed camera imaging. AE results revealed that although ESEM images show the occurrence of some micro-cracking before macro-cracking, so far it could not be detected by AE.

Abstract: A series of laboratory experiments were performed on synthetic fractures in gypsum and lucite to study the ratio of shear to normal fracture specific stiffness of a single fracture subjected to normal and shear stress. The specimens were made by placing two blocks in contact to form a fracture. The fracture surface was manufactured such that it was either well-mated or non-mated. For well-mated fracture surfaces, asperities were created by casting gypsum against sandpaper. After the first block hardened, the second block was cast against the rough surface of the first block. Non-mated fracture surfaces were fabricated with two lucite blocks that were polished (lucite PL) or sand-blasted (lucite SB) along the contact surface. In the experiments, each specimen was subjected to normal and shear loading while the fracture was probed with transmitted compressional and shear waves. Shear and normal fracture stiffnesses were calculated using the displacement discontinuity theory. The stiffness ratio determined from the experiments was compared to a theoretical ratio that was determined assuming that the transmission of compressional and shear waves was equal. The experimental results show that the fracture roughness of the non-mated fractures affects the stiffness ratio and that the shear fracture specific stiffness for well-mated fractures is sensitive to the applied shear stress.

Abstract: Cracking processes in rock specimens containing one, two or multiple artificial flaws under compression have been studied systematically and extensively in the laboratory for the past decades. To enhance our understanding of the role of en-echelon cracks in the formation of a shear rupture, specimens containing artificial en-echelon flaws are studied in this paper. Rock-like material Hydrocal-BII gypsum is used to mould block specimens, which contain en-echelon flaws cut by the Waterjet. The fracturing processes of the specimens under uniaxial loading are observed and recorded by a camcorder and a high speed video system. For the studied en-echelon flaws arrangement, three stages of fracture development are observed. The results show that tensile wing cracks (TWCs) are involved in coalescing the pre-existing flaws and fragmenting the bridge zones. The TWC development is strongly influenced by the stress field around adjacent flaw tips as indicated by the curvature of their crack paths. The development of a shear rupture across the entire specimen is attributed to the development of two short shear cracks emanating from the two outer flaw tips, which coalesce with two previously initiated steeply inclined tensile cracks.

ABSTRACT: The study of crack initiation and propagation is important for the understanding of rock mass behavior, which affects many rock engineering problems. Such studies can be done experimentally in the laboratory or in the field, or numerically. Here, a numerical study is presented, in which the stress and strain fields around a flaw tip were analyzed using the finite element code, ABAQUS, to better understand the processes involved in crack initiation and propagation. Double-flaw geometries were modeled with ABAQUS with the intent of identifying the differences between stress and strain fields around the flaw tip, relating the stress and strain fields to crack initiation and propagation, and comparing numerical results with those of tests performed on gypsum and marble specimens. Both stepped and coplanar flaw geometries were studied, as well as different stages of crack propagation were modeled based upon laboratory results. For the stepped flaws, both stress and strain field analyses correctly explain wing and shear crack initiation and propagation in gypsum and marble. Furthermore, the two analyses are also capable of describing reasonably well tensile and shear coalescence in gypsum and marble, respectively. For the coplanar flaws, it was found that the stress field analysis is capable of explaining wing crack initiation and propagation observed in tests on gypsum and marble. It is also capable of explaining shear coalescence observed in gypsum, but it is not capable of describing the indirect coalescence observed in marble. The strain field analysis is not only capable of satisfactorily explain what the stress field analysis explains, but it also correctly describes the indirect coalescence that occurs in marble specimens. 1. INTRODUCTION The study of crack initiation and propagation is important for the understanding of rock mass behavior which affects many rock engineering problems.

ABSTRACT: Owing to an increasing demand for water in the western provinces of Iran, the inevitability of dam construction on karstic foundations cannot be avoided; recent dams have been built on soluble, karstified, weathered, fractured, faulted, and folded rock foundations. To ensure the permanent stability of these dams, the first task is to investigate the characteristics of the underlying ground. The proposed Kangir dam site is located in western Iran (Elam Province). The geotechnical properties of soluble rocks at this site, as determined from laboratory tests, are the subject of this article. The foundation rocks comprise some limestones (Asamri Formation) and, to a greater extent, strata (Gachsaran Formation) containing marl, gypsum-bearing-marl, and gypsum. The lithomechanical characterization of the rocks included comprehensive engineering geology and rock mechanics studies conducted at the site including surface geology, jointing fabric study, borehole drilling and logging, and field and laboratory geotechnical testing. Laboratory tests on core samples were carried out to delineate the physical and geomechanical properties of the intact rock at the proposed dam site, using ASTM standards and ISRM suggested methods. 1. INTRODUCTION Water flowing through fractures in soluble rocks widens these through dissolution, a process known as karstification. Karstic terrain is a characteristic feature in the west of Iran along the Zagros Mountains because of vast areas of soluble rocks such as limestone and gypsum. Because of their flow pattern complexity, karst areas are considered problematic as construction sites for large dams. Owing to an increasing demand for water in the western provinces of Iran, dam construction on karstic foundations cannot be avoided; recent dams have been built on karstified, weathered, fractured, faulted, and folded foundations. To ensure the permanent stability of these dams, the first task is to investigate the characteristics of the underlying ground. In this article we highlight results of a comprehensive geotechnical and rock mechanics study carried out at the proposed Kangir dam site. This site is located in west of Iran (Elam Province) and will impound flow from the Kangir River. The study area is part of the folded Zagros area, a well-known active tectonic belt stretching north-west from south Iran. The foundation rocks comprise some limestones (Asamri Formation) and, to a greater extent, strata (Gachsaran Formation) that contain marl, gypsum-bearing-marl, and gypsum. Karstification is widespread in the limestone and gypsum units. Rock characterization included engineering geology and rock mechanics studies carried out at the site and surrounding areas, and included surface geology, jointing fabric study, borehole drilling and logging, and field and laboratory geotechnical testing. Laboratory tests on core samples were carried out to delineate the physical and geomechanical properties of the intact rock at the Kangir dam site. For the different rock units exposed in the study area, parameters such as dry density, saturated density, porosity, durability index, uniaxial compressive strength (UCS), shear and compressional wave propagation velocity (v S , v P ), and water absorption ratio were determined in the laboratory based on ASTM standards and ISRM suggested methods.

ABSTRACT: Uniaxial compression tests were conducted on prismatic Barre Granite specimens with two pre-cut, straight, open flaws. Using a high-speed video system, crack initiation, propagation, and coalescence were observed. Coalescence patterns for the granite specimens fit into a previous framework (developed for Molded Gypsum and Carrara Marble) except for one new coalescence pattern. The crack initiation stress and the maximum stress were measured for each specimen, and these results are interpreted, also. 1. INTRODUCTION Crack coalescence, which is the linkage of pre-existing flaws, is a common phenomenon in nature. The current study examined coalescence in Barre Granite as an extension of previous work presented by the MIT rock mechanics group [1]. A high-speed video system was used to record the coalescence of two artificial flaws in Barre Granite (the term flaw will be used in this paper to refer to an artificially made, pre-existing crack). This observation method made it possible to distinguish between shear and tensile cracks during their formation and propagation as well as record the sequence of cracks during coalescence. The observed coalescence behavior was complex, but also fit into the framework proposed earlier for Molded Gypsum and Carrara Marble [2]. 2. EXPERIMENTS 2.1. Specimen Preparation While this study used Barre Granite, several other materials have been used in the past being part of the continuing research of the MIT rock mechanics group. For nearly forty years, the group has studied the behavior of discontinuous (jointed) geo-materials [3]. In this context, a specific study began 17 years ago to experimentally investigate the effects of material type, geometric parameters, and loading conditions (Table 1) on fracture initiation, propagation, and coalescence [1, 4, 5, 6]. Bobet continued his work at Purdue University [7]. Several other groups have also researched crack coalescence in geo-materials [e.g. - 8, 9, 10]. To enable one to make comparisons between this study and previous work, similar procedures for specimen preparation were followed. Prismatic specimens of Barre Granite specimens with dimensions ~152 mm x~76 mm x~25 mm (6" x 3" x 1") were prepared. North Barre Granite, Inc. cut slabs ~25 mm (1") thick with a diamond saw. The other two dimensions (6" and 3") were cut with an OMAX waterjet, which cuts with a high-pressure mixture of water and a garnet abrasive. Two open, straight flaws 12.7 mm (0.5") long were cut in each specimen with the waterjet. The flaws were cut with different geometric relationships. Ligament length (L) was always equal to flaw length. The flaw inclination angle was varied (ß= 0°, 30°, 45°, 60°, and 75°) for two values of bridging angle (a= 0°?and 60°). As a consequence, flaw pairs were either coplanar (a= 0°) or left stepping (a= 60°) and could be nonoverlapping, partially overlapping, or completely overlapping. Three specimens were prepared and tested for each flaw-pair geometry. The two geometries summarized in Table 2 were geometries identical to those tested by Wong for Molded Gypsum and Carrara Marble [1]. Table 1. Parameters tested by the MIT rock mechanics group (both specimen parameters and loading conditions). Refer to Figure 1 for explanation of terms marked with an asterisk.(available in full paper)

ABSTRACT: The use of a high speed video system allows one to precisely observe the cracking mechanisms, in particular if shear or tensile fracturing is taking place. The present experimental study on gypsum and marble specimens confirmed that tensile wing cracks (TWCs) are in most cases the first cracks to appear in fracture propagation from existing flaws independent of aperture and material. The study, in addition, has shown that complex additional cracking occurs which depends on orientation of the existing flaws and material type. Either the TWCs or the other tip cracks produce failure. Also important is the formation of a process zone which could be visually observed in some marble experiments, but not in gypsum experiments. INTRODUCTION Systematic studies on prismatic pre-cracked molded Hydrocal-B11 gypsum specimens regarding crack propagation and coalescence patterns have been conducted over the past decades at MIT. They reveal that fracturing behavior is significantly influenced by the geometries of the pre-existing flaws (the term flaw is used in this paper to describe a pre-existing crack) [1, 2, 3, 4]. Similar experimental studies were also conducted by others on a variety of materials, including Columbia Resin 39 [5, 6, 7], glass [8, 9], plaster of Paris [10, 11], PMMA [12, 13], molded gypsum [14], sandstonelike molded barite [15, 16], sandstone-like concrete mix [17], and ice [18]. Experimental studies specifically on natural rocks included sandstone [12], granodiorite [19], limestone [19], granite [20], marble [20, 21, 22, 23]. In these studies, varying dimensions of prismatic specimens and cracks were studied. The specimen size ranged from 50mm x 32mm x 5mm [12] to 635mm x 279mm x 203mm [17]. The flaw length varied between 10mm and 50mm; and the flaw width (aperture) varied between 0.1 mm and 2mm. Due to the differences in the material (rock) types and flaw aperture sizes adopted in various studies, comparison of their results is difficult and was thus seldom attempted. For example, even though the same kind of tensile wing crack (TWC) can be identified in most of the experiments, its properties such as initiation angle and proximity to the flaw tips vary. In addition, several crack types are only reported in some experiments, but not in others. All these studies thus indicate that the influence of individual factors on the eventual fracturing processes and coalescence patterns is very complex and has not been fully understood. In order to better understand the fracture coalescence phenomena in natural rock and rocklike material, a systematic investigation on fundamental fracturing processes in prismatic specimens containing single flaws was conducted. Most importantly, this study relied on high speed videotaping of the fracturing process, which was not done in previous studies.

ABSTRACT ABSTRACT Deformational behavior of a rock mass can be modeled with a constitutive law based on theories of elasticity, and plastic and viscous deformation. For most rock types, such constitutive models may be used with confidence because there is no geochemical interaction between the rock-forming minerals and water. However, if volume changes in the rock due to geochemical phase transitions are predicted, then these volume changes must be converted into mechanical parameters and must be included into the constitutive laws. In this paper, geochemical phase transitions between anhydrite (CaSO 4 ) and gypsum (CaSO 4 .2H 2 0) will be brought to the attention of researchers in rock mechanics. Hydration of anhydrite to gypsum may yield volume increases up to 62.6 percent and dehydration of gypsum to anhydrite may cause volume decreases up to 38.5 percent. If one were to convert the volume increases in hydrating anhydrite into strains and calculates the required stresses to restrict the expansions, the magnitude of stresses will be found at GPa levels. Such stresses on swelling anhydrite layers cannot be provided by geologic media. Therefore, the host rocks will deform under these high stresses. On the other hand, under increasing stresses, geochemical transition of anhydrite to gypsum may stop after some hydration of anhydrite, and anhydrite and gypsum systems may become stable. Changes in temperature and solution compositions in the anhydrite/ gypsum system also control the stability of the geochemical system, and therefore, the extent of vol, me changes. A similar conceptual model can be drawn for volume decreases due to dehydration of gypsum to anhydrite. In this case, stress reduction on the gypsum layer may cause extensive fracturing and changes in the state of stress in the host rock mass. INTRODUCTION Evaporites have been reported from all continents, and approximately 25 percent of the continental areas are underlain by evaporitic rocks. Gypsum, anhydrite and halite are the most prominent minerals in evaporitic deposits. The original source of these evaporitic minerals is seawater. Precipitation of evaporitic minerals is usually generated either by direct evaporation of brine or by an indirect manner involving dissolution, transportation and reprecipitation of primary evaporitic deposits in waters circulating in the upper crust. Anhydrite and gypsum deposits generally occur in the vicinity of bedded and domal salt deposits. Phase transitions in calcium sulfate minerals are controlled by pressure, temperature and the composition of coexisting aqueous solutions. Phase diagrams showing the stability ranges of gypsum and anhydrite as a function of these parameters can be used to predict whether a hydration or a dehydration reaction could occur when environmental conditions in a rock system are changed. The geochemical stability of various anhydrite/gypsum systems and conceptual models for mechanical behavior of calcium sulfate bearing rock masses for their potential applications to tunnels, foundations and nuclear waste repositories in evaporitic rocks are discussed in the following paragraphs. GEOCHEMICAL ASPECTS OF HYDRATION/DEHYDRATION OF ANHYDRITE AND GYPSUM Solutions to the troublesome engineering problems associated with phase transformations of gypsum and anhydrite require basic information on the factors controlling the transition and on the geologic environment in which the transitions are likely to occur.

INTRODUCTION ABSTRACT Floor heave is a continuing problem in structures built upon black shale as a result of gypsum growth within the shales. This problem might be minimized by periodic injections of powerful crystallization inhibitor chemicals into the vicinity of potential gypsum growth within the shales. In order to determine if this approach might be productive, the effect of sulfate scale inhibitory compounds upon the nucleation and growth of gypsum was investigated in laboratory systems simulating the acidic black shale heave environment. Of more than 25 different commercial and research inhibitors tested, nearly all reduced gypsum nucleation and growth under neutral pH conditions, but only three were even moderately effective at a pH of 2.5, similar to the acidity of black shale heave environments. At pH 2.5, however, many of the additives modified crystal growth morphology and size. Testing of expansion within rock cores in a consolidometer during induced gypsum growth within the cores showed that several additives modified the rate of expansion, apparently as a result of effects upon crystallization force pressures through habit modifications of growing gypsum crystals. These preliminary results suggest that periodic applications of crystallization inhibitor chemicals may be a viable approach to minimizing black shale heave. Heaving of floor slabs and lightly loaded structures built on black pyritic shales is a construction engineering problem in many locations, including Norway, the United States, and Canada (Quigley, etal., 1973). The cause of the heave has been documented by many workers, including Grattan-Bellew and Eden (1975); Penner, Gillott, and Eden (1970); and Quigley and Voran (1970). These researchers agree that the growth of gypsum, CaS0 4 .2H 2 0, is chiefly responsible. Although often there is little or no gypsum in the original shale, once a structure has been built on the pyritic shales, conditions often develop which lead to its growth. Sulfate ions are generated by the oxidation of pyrite or marcasite, FeS 2 , and these ions react with available calcium ions from the dissolution of calcium-bearing minerals in the acid shales to form gypsum. The continued growth of gypsum eventually leads to shale expansion, in a manner similar to that in frost-induced soil expansion. As soon as overlying concrete slabs are cracked as a result of initial shale expansion, pressure of the shale in the heaved region is reduced and a pressure gradient may accelerate the migration of dissolved calcium and sulfate into the region of gypsum growth; this leads to an increased rate of shale heave. Although there are potentially several different approaches in attempting to minimize or eliminate heave due to gypsum growth within black shales, one of the most economically attractive methods involves the inhibition, or prevention, of gypsum growth by chemical means. Conventional methods, such as sealing of foundation rocks to prevent pyrite oxidation, can be readily applied to new constructions, but heave alleviation beneath already existing structures is expensive. Other different approaches suggested to deal with this problem, such as floor bolting, backfill, or coating the underfloor with an impervious surface, all have limited applications.

ABSTRACT ABSTRACT The use of rock mechanics techniques in the reappraisal of the mining dimensions of a gypsum mine as it was developed is described. The behaviour of the roof strata, under complex geological circumstances, was identified to be that of the "linear arch" structure. Model tests were carried out to provide numerical data for use in future mine design. I INTRODUCTION The optimum exploitation of a mineral deposit is the result of continual refinement of the many aspects of minerals engineering. One such aspect is the detailed method of actually mining the raw mineral material. Before the choice of method and the detailed application of the system can be made, the deposit must be examined for all potential problems. Based on this data a preliminary design for the mine can be implemented, using past experience, theoretical analysis and laboratory testing. In view of the fact that rock deviates from the theoretical assumptions used in predicting its behaviour, the preliminary design requires the use of a substantial safety factor. This implies the wastage of man and material in providing additional support. Ideally, as mining progresses, and the behaviour of the mine design becomes known, changes to the design can be made to reduce the safety factor where desirable, whilst continuing to maintain a satisfactory safety standard. This aim can be achieved constructively by employing various rock mechanics investigational techniques to attain an optimum mining dimension and hence in the mineral exploitation. The subject of this paper is to illustrate how such techniques were used in the re-appraisal of a gypsum mine and in the appreciation of a complex and unforseen set of geological circumstances. II GENERAL CONSIDERATIONS AND MINING PARAMETERS Rock mechanics research has been carried out by the Department of Mining Engineering at the University of Newcastle upon Tyne, England at British Gypsum''s Sherburn mine since its initial development in 1966.